2024 TJC Prelims H1 Paper 2 Structured QP

8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS CENTRE NUMBER S INDEX NUMBER Chemistry 8873/02 Paper 2 Structured Questions 21 August 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and class in the spaces provided at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in bracket [ ] at the end of each question or part question. This document consists of 26 printed pages and 2 blank pages. For Examiner’s Use MCQ / 30 Section A Q1 / 8 Q2 / 8 Q3 / 12 Q4 / 10 Q5 / 10 Q6 / 12 Section B Q7 / 20 Q8 / 20

2 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section in the spaces provided. 1 This question is about copper-containing species. (a) Copper can exist as a number of isotopes. Some copper isotopes are unstable but are potentially useful for nuclear medicine. Complete Table 1.1 for two isotopes of copper. Table 1.1 isotopes protons neutrons electrons 63 29Cu 38 [2] (b) Tumbaga is an alloy of copper and gold. A sample of tumbaga was analysed and the composition of the isotopes present in the sample are shown in Table 1.2. Table 1.2 Mass number % abundance 63 56.4 65 x 197 18.5 (i) Determine the percentage abundance, x, of the species of mass number 65. [1] (ii) Hence, calculate the relative atomic mass, Ar, of the copper present in this sample of tumbaga. [1]

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (c) Brass is an alloy of copper and zinc. The percentage of mass of copper varies from 50% to 85%, depending on the properties needed in the alloy. A series of reactions is carried out in the laboratory to determine the percentage of copper in a sample of brass. 0.30 g of brass is dissolved in acid to give 100.0 cm3 of solution in which all copper is present as Cu 2+ ions. 25.0 cm 3 of the solution is transferred to a conical flask using a pipette and reacted with excess potassium iodide, K I. All the copper is precipitated as Cu I solid and iodine is formed. The iodine requires 21.50 cm3 of 0.0400 mol dm-3 S2O32- to reach the end- point of titration. 2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq) I2(aq) + 2S2O32-(aq) → 2I–(aq) + S4O62-(aq) (i) Determine the number of moles of iodine reacted with S2O32- in the titration. [1] (ii) Use your result in (c)(i) to calculate the number of moles of Cu 2+(aq) in 100.0 cm3 of the solution. [1] (iii) Hence, determine the percentage by mass of copper in this sample of brass. [2] [Total: 8]

4 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 2 Phosgene, Cl2C=O, is a colourless, toxic gas. It is used in the production of pesticides, rubbers and adhesives. (a) (i) State the shape of a phosgene molecule. ..................................................................................................................................[1] (ii) The molecule of phosgene contains both σ (sigma) and π (pi) bonds. Draw labelled diagrams to show how orbitals overlap to form • a σ (sigma) bond • a π (pi) bond. [2] (b) Table 2.2 shows the electronegativity values of the atoms in phosgene. Table 2.2 atom electronegativity / Pauling units carbon 2.5 chlorine 3.0 oxygen 3.5 (i) Explain what is meant by the term electronegativity. ...................................................................................................................................... ..................................................................................................................................[1]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over (ii) Using the information in Table 2.2, deduce whether phosgene is a polar molecule. Explain your answer. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ..................................................................................................................................[2] (c) Phosgene reacts with methylamine to form methyl isocyanate. Cl2C=O + CH3NH2 CH3NCO + 2HCl methylamine methyl isocyanate (i) Draw a dot -and-cross diagram to show the bonding present within a methylamine molecule. [1] (ii) In the presence of a catalyst, methyl isocyanate reacts with itself to form compound A, which is a non-polar molecule. 3CH3NCO(g) C6H9N3O3(s) A Suggest why, at room temperature, methyl isocyanate is a gas but A is a solid. ...................................................................................................................................... ..................................................................................................................................[1] [Total: 8]

6 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 3 (a) Magnesium, aluminium and phosphorus are elements in Period 3 of the periodic table. (i) State the electronic configuration of aluminium. ..................................................................................................................................[1] (ii) State and e xplain the difference in first ionisation energies of aluminium and magnesium. ...................................................................................................................................... ...................................................................................................................................... ..................................................................................................................................[2] (iii) Write a balanced equation for the reaction of phosphorus(V) oxide with excess water. ..................................................................................................................................[1] (b) Phosphoric(V) acid, H3PO4, is a weak Bronsted-Lowry acid. In a reaction where it behaves as an acid, phosphoric(V) acid can donate one, two or three protons. (i) Explain the meaning of the term weak Bronsted-Lowry acid. ...................................................................................................................................... .............................................................................................................................